APRS is a pneumonic for Automatic Position Reporting System.  It was developed by WB4APR, Bob Bruninga.  The purpose of APRS is simply to transmit position, status, and messages to other amateur radio operators.  This can be accomplished directly (point to point), over a digipeater (retransmits packets over a wide area), by IGATES (forwarding packets to and from the internet), and various other methods that are discussed on this site.

Here is what Bob has to say about APRS:

"APRS is different from regular packet in four ways. First by adding maps and other data displays, second by doing all communications using a one-to-many protocol so that everyone is updated in real time, third by using generic digipeating so that prior knowledge of the network is not required, and forth, since 1997, a worldwide transparent Internet backbone, linking everyone worldwide. APRS turns packet radio into a real-time tactical communications and display system for emergencies and public service applications (and global communications). Normal packet radio has only shown usefulness in passing bulk message traffic (Email) from point to point. It has been difficult to apply conventional packet to real time events where information has a very short life time.

Although the recent interfaces to the Internet make APRS a global communications system for live real-time traffic, this is not the primary objective. But like all of our other radios, how we use APRS in an emergency of special event is what drives the design of the APRS protocol. Although APRS is used 99% of the time over great distances, the protocol will always be optimized for short distance real-time crisis operations.

APRS provides universal connectivity to all stations by avoiding the complexity and limitations of a connected network. It permits any number of stations to exchange data just like voice users would on a voice net. Any station that has information to contribute simply sends it, and all stations receive it and log it. Secondly, APRS recognizes that one of the greatest real-time needs at any special event or emergency is the tracking of key assets. Where is the Event Leader? Where are the emergency vehicles? What's the Weather at various points in the County? To answer these questions, APRS is a full featured automatic vehicle location and status reporting system too. It can be used over any 2-way radio system including HAM, CB, Marine Band, and Cellular Phone."

Bob Bruninga, WB4APR